What your Vaillant boiler error code means

We have created a comprehensive list of all Vaillant boiler error codes sorted by the model type. Just click on your boiler model below and you will be taken to a list of all the fault codes related to that boiler.

Our Vaillant boiler error code list is meant as a guide only to help you understand what the issue is and assess how much it would be likely to cost to fix it. Remember, it is important that you never attempt to fix an issue within your boiler if you aren’t a Gas Safe registered engineer.

Looking for a particular boiler? Use the links below to jump straight to it:

1. Vaillant EcoMax Pro 18/28E Error Codes
   

    

2. Vaillant EcoTEC 65kW Error Codes
   

    

3. Vaillant EcoTec Plus / Ecotec Pro Error Codes
   

    

4. Vaillant Turbomax Plus 824/828E Error Codes
   

    

5. Vaillant Ecomax Pro 828E Error Codes

    

Vaillant EcoMax Pro 18/28E Error Codes

The EcoMax pro are regular boilers. Regular boilers are also known as open vent boilers because they are linked to an outside vent. The system provides central heating and hot water by using both a storage cylinder and water tank, which gives ultra-efficient operation. Due to the open vent they are not pressurised.

This boiler was manufactured in 2003 and is not currently in production.

Vaillant F.1 Boiler Fault Code

Error Description
Failure to ignite.

Error Cause
Lack of gas, a fault with the ignition or flue, or you may need to adjust the gas valve or replace a defective electrode lead.

Fix Vaillant F.1 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.
 

Vaillant F.4 Boiler Fault Code

Error Description
Failure to ignite/ignition fault

Error Cause
• Insufficient gas supply.
• Incorrect gas valve adjustment
• Electrode defect
• Ignition lead defect
• Electronic igniter defective

Fix Vaillant F.4 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.
 

Vaillant F.5 Boiler Fault Code

Error Description
System has overheated and locked out as a safety measure

Error Cause
• Overheat stat operated
• Maximum temperature exceeded
• Thermistor connections
• Air in system with thermistor at maximum setting
• Faulty overheat stat connection

Fix Vaillant F.5 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.
 

Vaillant F.6 Boiler Fault Code

Error Description
Central heating flow NTC fault

Error Cause
• Flow NTC cable defective/broken NTC faulty
• Flow thermistor not fitted correctly
• Check pipework configuration

Fix Vaillant F.6 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.
 

Vaillant F.17 Boiler Fault Code

Error Description
Electrical supply less than 170v

Error Cause
• Check electrical supply / polarity
• Check fan

Fix Vaillant F.17 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.
 

Vaillant F.24 Boiler Fault Code

Error Description
Indicates an issue arising from your boiler’s pump or pump supply.

Error Cause
• System fault
• Possible external pump failure
• Check NTC on return
• Check that the pump is wired into the appliance and not from the programmer

Fix Vaillant F.24 Error Code
A Gas Safe engineer will need to take a look and see what’s causing the issue to occur.

Vaillant EcoTEC 65kW Error Codes

This appliance is a Combination boiler (combi) with additional water storage capacity. This means it heats water when you draw a tap. It doesn't need a water storage tank or a cylinder because the boiler's connected directly to the water mains, heating water as needed.

Lightweight for its class with a compact design and a comprehensive range of flues, fittings and accessories, the ecoTEC boiler can be sited almost anywhere. This boiler is no longer in production.

Vaillant EcoTec Plus / Pro Error Codes

The Vaillant ecoTEC plus 800 series is a condensing combination boiler that is currently in production. This appliance is a Combination boiler (combi). This means it heats water when you draw a tap. It doesn't need a water storage tank or a cylinder because the boiler's connected directly to the water mains, heating water as needed.

The Vaillant ecoTEC Pro comes as a combi, system or heat only. The Vaillant Plus and Pro both use the same error codes.

This boiler was first manufactured in 2016 and is still in production.

Vaillant F.00 Boiler Fault Code

Error Description
This fault according to the Vaillant Instructions and Servicing manual is a Heating Flow Temperature Sensor interruption or Heating Flow NTC Thermistor fault.

Error Cause
NTC (Negative Temperature Coefficient) plug not plugged in or has come loose, multiple plug on the PCB (Printed Circuit Board) not plugged in correctly, interruption in cable harness, NTC defective.

Fix Vaillant F.00 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.01 Boiler Fault Code

Error Description
Return temperature sensor interruption.

Error Cause
NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective

Fix Vaillant F.01 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.02 Boiler Fault Code

Error Description
Interruption cylinder charging sensor (NTC) only in combination with F.91 error

Error Cause
NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on actoSTOR electronics

Fix Vaillant F.02 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.03 Boiler Fault Code

Error Description
Interruption cylinder sensor actoSTOR (NTC) only in combination with F.91

Error Cause
NTC defective, NTC cable defective, defective plug connection on NTC, defective plug connection on actoSTOR electronics

Fix Vaillant F.03 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.10 Boiler Fault Code

Error Description
Flow NTC short circuit

Error Cause
NTC defective, short circuit in cable harness, cable/casing

Fix Vaillant F.10 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.11 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is a Heating Flow NTC Thermistor Fault or Heating Return NTC short circuit

Error Cause
There Is A Short Circuit On The Heating Return NTC Thermistor (Should Read 12Kohms @ 20C). Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB.

Fix Vaillant F.11 Error Code
Check the NTC sensor. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary.
 

Vaillant F.12 Boiler Fault Code

Error Description
Short circuit at cylinder charging sensor (NTC) only in combination with F.91

Error Cause
Sensor plug has a mass short to the casing. Short-circuit in wiring loom. Sensor faulty

Fix Vaillant F.12 Error Code
There is an issue with your heating flow thermister (NTC) and sensor plug, wiring loom and sensor will need to be tested for errors.
 

Vaillant F.13 Boiler Fault Code

Error Description
VU-/VUW boiler: Short circuit warm start sensor/cylinder sensor VUW boiler with actoSTOR: Short circuit cylinder sensor (NTC) only in combination with F.91

Error Cause
NTC defective, short circuit in cable harness, cable/casing

Fix Vaillant F.13 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.20 Boiler Fault Code

Error Description
Safety switch-off: temperature limiter

Error Cause
Your boiler is overheated and needs to cool down

Fix Vaillant F.20 Error Code
Turn your boiler off and let it cool down.
 

Vaillant F.22 Boiler Fault Code

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective

Fix Vaillant F.22 Error Code
1.Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system.
2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
3. Check that the pump connection is not loose. If necessary remove the connection from the connector, check and re-insert.
 

Vaillant F.23 Boiler Fault Code

Error Description
Safety switch-off: Temperature difference too great

Error Cause
• Inadequate Pump Operation
• Blockage Or Air Lock Within The Appliance (No Water Movement)
• Blockage Or Air Lock In The Heating System (No Water Movement)
• Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
• Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C)

Fix Vaillant F.23 Error Code
Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.
 

Vaillant F.24 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)

Error Cause
• Inadequate Pump Operation
• Isolation Valves Closed Under The Appliance
• Blockage Or Air Lock Within The Appliance (No Water Movement)
• Blockage Or Air Lock In The Heating System (No Water Movement)
• Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
• Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C)

Fix Vaillant F.24 Error Code
Check the isolation valves are open under the boiler.

Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary
 

Vaillant F.25 Boiler Fault Code

Error Description
The EcoTEC Plus F.25 error is a safety shut-off function.  In this case the flue gas temperature is too high. 

Error Cause
The Ecotec Plus boilers have a flue gas temperature limiter known as STB.  Either this limiter is faulty, sooted up and needs cleaning or replacing. Other causes may be the plug has broken off or the cable harness is faulty.

Fix Vaillant F.25 Error Code
Check the STB, clean and retest. If issue persists, replace limiter. Test plug and cable harness for issues.
 

Vaillant F.27 Boiler Fault Code

Error Description
According to the installation and servicing instructions manual, “safety switch-off: Flame simulation”.  Also according to other sources, “Incorrect Flame Detection Fault (Flame Detection Even Though The Gas Valve Is Off)”

Error Cause
• Damage On The Electrode Or The Ignition Lead
• Moisture Present On The Electronics
• Fault On The Spark Generator
• Fault On The Main PCB

Fix Vaillant F.27 Error Code
Check for moisture on electronics or PCB. Test spark generator, electrode and ignition lead. Replace if any issues detected/
 

Vaillant F.28 Boiler Fault Code

Error Description
Failure during start-up: ignition unsuccessful.

Error Cause
• Gas meter defective or gas pressure regulator has triggered,
• Air in gas
• Gas flow pressure too low
• Thermal isolator device (TAE) has triggered
• Condensate duct blocked
• Incorrect gas restrictor
• Incorrect ET gas valve
• Fault on the gas valve
• Multiple plug on PCB incorrectly plugged in
• Break in cable harness
• Ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective

Fix Vaillant F.28 Error Code
There are a range of issues that can cause an F.28 error code to occur, if you encounter this issue - first check to ensure gas is coming into your property. If it is then call a Gas Safe engineer to test your system and isolate the fault.
 

Vaillant F.29 Boiler Fault Code

Error Description
Failure during operation: Re-ignition unsuccessful

Error Cause
Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure.

Fix Vaillant F.29 Error Code
Check the gas supply into the property. If gas is coming into property then call a Gas Safe engineer to identify the issue. If gas isn’t coming into the property check with your gas provider.
 

Vaillant F.32 Boiler Fault Code

Error Description
Fan Fault

Error Cause
Plug at fan not correctly plugged in, multiple plug on PCB not correctly plugged in, break in cable harness, fan blocked, Hall sensor defective, electronics defective

Fix Vaillant F.32 Error Code
Call a Gas Safe engineer to identify the issue. There are a number of issues that could lead to the fan not working.
 

Vaillant F.35 Boiler Fault Code

Error Description
This fault code suggest that there is a problem along the Air/Flue route. According to the manufacturer's instructions, the exact meaning is that there is an ‘air/flue gas duct fault’.

Error Cause
The flue is blocked.

Fix Vaillant F.35 Error Code
Check there are no obstructions to the flue either internally or externally. If there are no obstructions then there could be a blockage located on the fan.
 

Vaillant F.42 Boiler Fault Code

Error Description
The F42 Fault’s cause is that of a short circuit / interruption in the coding resistor output range that can be located in the cable harness at the heat exchanger or the gas group resistor on the PCB.

Error Cause
Issue between the coding resistor and the PCB.

Fix Vaillant F.42 Error Code
Check all the connections between the coding resistor and the PCB, using a multimeter if necessary. This fault can occur in combination and possibly due to F.70.
 

Vaillant F.49 Boiler Fault Code

Error Description
eBUS fault.

Error Cause
Short circuit on the eBUS, eBUS overload or two power supplies with different polarities on the eBUS.

Fix Vaillant F.49 Error Code
Do not attempt to fix this fault yourself. Call a Gas Safe engineer.
 

Vaillant F.52/F.53 Boiler Fault Code

Error Description
The F.52 and F.53 fault codes indicate a fault with the mass flow sensor, that is located just behind the gas valve connecting to the fan on Vaillant Ecotec boilers. There may be several causes of this fault, either mechanical or electrical. 

Error Cause
The meaning of F.52 is that there is a connection fault of the sensor. The meaning of F.53 is that the flow sensor function is faulty, or the filter cap is wet, filter cap is blocked or gas flow pressure too low.

Fix Vaillant F.52/F.53 Error Code
In order to repair this fault, you may need to check that the sensor is connected correctly. Simply remove it and plug it back in. This will most likely address an F.52 fault code. 

In order to fix an F.53 fault code you may have to electrically test the functioning of the sensor and it’s output values, using readings available from Vaillant technical. An engineer can check it electrically, and if necessary replace this part. If the part is functioning properly, there may be a possibility that either the gas supply is too low or the PCB is at fault. 

Gas supply pressure can be checked by a gas heating engineer using gas testing equipment. Gas appliance repairs should be carried out by Gas Safe Register listed professionals.
 

Vaillant F.54 Boiler Fault Code

Error Description
This fault code suggests there is a fault in the gas supply. Usually this fault is accompanied by an F.28 or F.29 Fault code.

Error Cause
According to Vaillant, there is insufficient gas supply to operate the unit. Gas isolator may be closed on the boiler or elsewhere. Also gas flow pressure may be too low.

Fix Vaillant F.54 Error Code
Check if the gas stop cock is fully open at the meter, near the boiler or anywhere else there may be any additional stop cocks.

Check valve is working as it should. Solenoid testing equipment and multimeters may be required. If found faulty, a replacement gas valve would be required.
 

Vaillant F.56 Boiler Fault Code

Error Description
Fault: Mass flow sensor regulation

Error Cause
Gas valve defective, cable harness to gas valve defective.

Fix Vaillant F.56 Error Code
Check gas valve is working as it should. Solenoid testing equipment and multimeters may be required. If found faulty, a replacement gas valve would be required.
 

Vaillant F.57 Boiler Fault Code

Error Description
Fault during comfort safety mode

Error Cause
The Ignition electrode is highly corroded.

Fix Vaillant F.57 Error Code
Remove the ignition electrode to inspect it without opening up the main heat exchanger. Turn off the boiler. Remove the front panel. Unplug the ignition cable from the ignition electrode including the earth connector. Undo the two screws either side. Remove the electrode assembly. Inspect the electrode and replace as necessary.
 

Vaillant F.61 Boiler Fault Code

Error Description
Gas valve actuation fault

Error Cause
• Cable harness supply line to the gas valve is defective (short to earth, short circuit)
• Gas valve defective
• PCB defective

Fix Vaillant F.61 Error Code
Check the resistance across the gas valve for 50-54 ohms(+/-10%). If this is correct, then likely the PCB needs to be replaced.

If the gas valve fails the resistance test, then likely the gas valve needs to be replaced.
 

Vaillant F.62 Boiler Fault Code

Error Description
Gas valve switch-off delay

Error Cause
• Delayed shutdown of gas valve detected– Secondary light (ignition and monitoring electrode indicates delayed extinguishing of the flame signal)
• Gas valve defective
• PCB defective

Fix Vaillant F.62 Error Code
Carry out a local tightness test on the gas valve. If gas tight then you may have to replace the PCB or replace the gas valve.
 

Vaillant F.63 Boiler Fault Code

Error Description
If you have a F63 fault code displayed on your Vaillant boiler, there is a problem with the circuit board (PCB). The PCB is what communicates with all electronic components.

Error Cause
• Old age; general wear and tear
• Connections to and from the PCB have worked loose, or have been damaged
• The PCB has not been setup correctly by a service engineer after a service, new boiler, or new PCB installation

Fix Vaillant F.63 Error Code
Usually this will require a new PCB which can cost between £350-£450. You may want to consider replacing your boiler if it is getting on in years.
 

Vaillant F.64 Boiler Fault Code

Error Description
If you have a F63 fault code displayed on your Vaillant boiler, there is a problem with the electrics. NTC thermistors on the flow and return boiler pipes. Faulty connections. PCB fault

Error Cause
• Short-circuit in flow
• Return NTC
• Electronics defective

Fix Vaillant F.64 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.65 Boiler Fault Code

Error Description
Main PCB Temperature Too High

Error Cause
• Mains Input Voltage Problem
• Damaged Or Loose Electrical Connection On The Main PCB
• Main PCB Fault

Fix Vaillant F.65 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.67 Boiler Fault Code

Error Description
Flame Signal Fault On The Main PCB

Error Cause
• Damaged Or Loose Electrical Connection On The Main PCB
• Main PCB Fault
• Mains Input Voltage Problem (Reverse Polarity, Poor Earth Etc)

Fix Vaillant F.67 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.68 Boiler Fault Code

Error Description
Unstable flame signal fault

Error Cause
• Insufficient Inlet Working Gas Pressure To The Appliance
• Flue Problem
• Incorrect Gas Valve Adjustment (Poor Combustion)
• Debris Within The Heat Engine (Burner Etc)
• Electrode Or Ignition Lead Fault
• Spark Generator Fault
• Faulty Gas Valve

Fix Vaillant F.68 Error Code
As the F.68 error code can be linked to a number of issues, you will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.70 Boiler Fault Code

Error Description
Invalid device specific number (DSN)

Error Cause
The cause of this error is usually that the PCB which is the same across many models has not been assigned its software identity for the model of boiler it is intended for. If the PCB is not assigned this number it cannot operate safely therefore it produces an F.70 error.

Fix Vaillant F.70 Error Code
Testing will need to be carried out on your PCB to see whether it’s a malfunction and needs replacing or whether DNS can be assigned through the engineer interface.
 

Vaillant F.71 Boiler Fault Code

Error Description
Heating Flow NTC Thermistor Disconnected Or Defective (No Temperature Change When Burner Lit).

Error Cause
• Heating Flow NTC Thermistor Is Not Connected To The Flow Pipe On The Main Heat Exchanger Correctly
• Defective Heating Flow NTC Thermistor

Fix Vaillant F.71 Error Code
A gas engineer will first need to check that wiring hasn’t become disconnected, and that the NTC thermistor is connected to the main heat exchanger.

To determine this, it’s a simple case of a visual check. If this is the issue, luckily, it’s an easy one to fix. The engineer simply needs to connect the NTC thermistor to the main heat exchanger.

But, they’ll also need to check the state of wiring. Any damaged wiring will cause intermittent signals to the PCB. And, this might mean the thermistors are signalling lack of water temperature, even if that’s not the case.
 

Vaillant F.72 Boiler Fault Code

Error Description
According to Vaillant, the F72 fault code is a NTC thermistor fault.

There is a permanent temperature difference between the flow and return NTC thermistors, causing the F72 error to be displayed.

Error Cause
• An incorrect resistance reading on the flow and return thermistors
• A wiring issue between the NTC thermistor and the PCB
• Thermistors that have been fitted to the incorrect pipes

Fix Vaillant F.72 Error Code
A gas engineer will first need to check that wiring hasn’t become disconnected, and that the NTC thermistor is connected to the main heat exchanger. A replacement thermister will only cost £10-£30 for the part and additional labour costs.
 

Vaillant F.73/F.74 Boiler Fault Code

Error Description
Water pressure sensor signal in the wrong range (too low)

Error Cause
• A loose, broken or damaged connection between the sensor and the PCB
• A connection that has water damage somewhere between the sensor and main PCB
• A faulty low water pressure sensor

Fix Vaillant F.73/F.74 Error Code
A gas engineer will need to check the wiring to the water pressure sensor and the sensor itself for faults. If a new sensor is required it’s likely to cost £50 in addition to labour costs.
 

Vaillant F.75 Boiler Fault Code

Error Description
No pressure change detection when starting-pump.

Error Cause
The number one cause of this fault is some sort of blockage or has caused a component to fail. When diagnosing which component has failed, you need to check for the presence of sludge. If there is sludge, this should be cleaned out or system powerflushed before changing components.

Fix Vaillant F.75 Error Code
A gas engineer will need to check the system to identify whether there is a blockage in your boiler or system. A powerflush may be required if a blockage is identified. Checking pump seals and pump is another fix for this error.
 

Vaillant F.76 Boiler Fault Code

Error Description
Overheating protection on primary heat exchanger has responded

Error Cause
Cable or cable connections for safety fuse in primary heat exchanger or primary heat exchanger defective

Fix Vaillant F.76 Error Code
A gas engineer will need to check the connections leading to the heat exchanger. If the heat exchanger has cracked then it’s an expensive job and you may want to consider looking at a boiler replacement.
 

Vaillant F.77 Boiler Fault Code

Error Description
Flue non-return flap/condensate pump fault

Error Cause
Blockage to condensate pump or malfunction of condensate pump

Fix Vaillant F.77 Error Code
A gas engineer will need to check the condensate pump for a blockage and clear if there is one. In the case of no blockage, a new condensate pump will be required.
 

Vaillant F.83 Boiler Fault Code

Error Description
Flow and/or return temperature sensor temperature change fault

Error Cause
When the burner starts, the temperature change registered at flow and/or return temperature sensor is non-existant or too small. Not enough water in the boiler. Flow and/or return temperature sensor not in correct position at pipe

Fix Vaillant F.83 Error Code
There are a range of issues that could trigger an F.83 boiler fault from a leak in your system to a sensor error. You will need to call in a professional to diagnose what the cause of the error is.
 

Vaillant F.84 Boiler Fault Code

Error Description
According to Vaillant, the F.84 fault code will be displayed due to a temperature difference on the NTC flow/return thermistors that is permanent.

Error Cause
• Flow and return temperature sensors return implausible values
• Flow and return temperature sensors have been inverted
• Flow and return temperature sensors have not been correctly fitted

Fix Vaillant F.84 Error Code
Check the thermisters are installed correctly and are working. Check the PCB to ensure there is no malfunction in reading the thermisters.
 

Vaillant F.85 Boiler Fault Code

Error Description
Flow and return temperature sensors incorrectly fitted

Error Cause
Flow and/or return temperature sensors have been fitted to the same pipe/wrong pipe

Fix Vaillant F.85 Error Code
An engineer will manually check readings for both temperature and resistance.

Your Vaillant boiler should be providing a 12k ohms reading at 20C. If it’s not, there’s either a problem with the thermistor, or the wiring.

The engineer will need to use a multimeter to test all sections of the wiring, wired connections and each of the two NTC thermistors independently. Just because one thermistor is faulty, doesn’t mean the other is.

If there is an issue with a thermister then it’s a minor replacement job and should cost in the region of £150-£250 with labour included.
 

Vaillant F.92 Boiler Fault Code

Error Description
Coding resistor fault

Error Cause
The coding resistor on the PCB does not match the entered gas family.

Fix Vaillant F.92 Error Code
Check the resistor, repeat the gas family check and enter the correct gas family.
 

Vaillant F.93 Boiler Fault Code

Error Description
Gas group fault

Error Cause
Combustion quality outside the permitted range:
Wrong gas restrictor, recirculation, wrong gas family, internal pressure measuring point in venturi blocked (do not use lubricant on O-ring in venturi).
Gas family check prematurely terminated.

Fix Vaillant F.93 Error Code
There are a range of issues that could trigger an F.93 boiler fault. You will need to call in a professional to diagnose what the cause of the error is.

Vaillant Turbomax Plus 824/828E Error Codes

The Vaillant turboMAX plus series boilers are standard efficiency combi boilers that are not in production. This appliance is a Combination boiler (combi). This means it heats water when you draw a tap. It doesn't need a water storage tank or a cylinder because the boiler's connected directly to the water mains, heating water as needed

This boiler was first manufactured from 2000 to 2008 and this particular model is no longer being produced. 

Vaillant F.00 Boiler Fault Code

Error Description
This fault according to the Vaillant Instructions and Servicing manual is a Heating Flow Temperature Sensor interruption or Heating Flow NTC Thermistor fault.

Error Cause
NTC (Negative Temperature Coefficient) plug not plugged in or has come loose, multiple plug on the PCB (Printed Circuit Board) not plugged in correctly, interruption in cable harness, NTC defective.

Fix Vaillant F.00 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.01 Boiler Fault Code

Error Description
Return temperature sensor interruption.

Error Cause
NTC plug not plugged in or has come loose, multiple plug on the PCB not plugged in correctly, interruption in cable harness, NTC defective

Fix Vaillant F.01 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.10 Boiler Fault Code

Error Description
Flow NTC short circuit

Error Cause
NTC defective, short circuit in cable harness, cable/casing

Fix Vaillant F.10 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.11 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is a Heating Flow NTC Thermistor Fault or Heating Return NTC short circuit

Error Cause
There Is A Short Circuit On The Heating Return NTC Thermistor (Should Read 12Kohms @ 20C). Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB.

Fix Vaillant F.11 Error Code
Check the NTC sensor. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary.
 

Vaillant F.13 Boiler Fault Code

Error Description
VU-/VUW boiler: Short circuit warm start sensor/cylinder sensor VUW boiler with actoSTOR: Short circuit cylinder sensor (NTC) only in combination with F.91

Error Cause
NTC defective, short circuit in cable harness, cable/casing

Fix Vaillant F.13 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.20 Boiler Fault Code

Error Description
Safety switch-off: temperature limiter

Error Cause
Your boiler is overheated and needs to cool down

Fix Vaillant F.20 Error Code
Turn your boiler off and let it cool down.
 

Vaillant F.22 Boiler Fault Code

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective.

Fix Vaillant F.22 Error Code
1.Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system.
2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
3. Check that the pump connection is not loose. If necessary remove the connection from the connector, check and re-insert.
 

Vaillant F.24 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is Water Circulation Fault (Temperature Rise Greater Than 10 Degrees Celcius Per Second)

Error Cause
• Inadequate Pump Operation
• Isolation Valves Closed Under The Appliance
• Blockage Or Air Lock Within The Appliance (No Water Movement)
• Blockage Or Air Lock In The Heating System (No Water Movement)
• Check Domestic Hot Water Heat Exchanger and Domestic Hot Water Heat Exchanger Filter For Debris If Fault Occurs On Hot Water Mode Only
• Check Resistance On The Heating Flow & Return NTC Thermistors To Ensure Accurate Temperature Monitoring (Should Read 12K ohms @ 20C)

Fix Vaillant F.24 Error Code
Check the isolation valves are open under the boiler.

Check the Flow and return NTC sensors. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary dependent on checks.

Make sure there are no blockages in the pipework.  If there is debris in the system, flushing may be required. Then individual components may require cleaning or replacing dependent on damage caused by debris.  You may need to activate the pump purge program (see P Codes). Also check the domestic heat exchanger is free of debris, cleaning the filter as necessary.
 

Vaillant F.28 Boiler Fault Code

Error Description
Failure during start-up: ignition unsuccessful.

Error Cause
• Gas meter defective or gas pressure regulator has triggered,
• Air in gas
• Gas flow pressure too low
• Thermal isolator device (TAE) has triggered
• Condensate duct blocked
• Incorrect gas restrictor
• Incorrect ET gas valve
• Fault on the gas valve
• Multiple plug on PCB incorrectly plugged in
• Break in cable harness
• Ignition system (ignition transformer, ignition cable, ignition plug, ignition electrode) defective

Fix Vaillant F.28 Error Code
There are a range of issues that can cause an F.28 error code to occur, if you encounter this issue - first check to ensure gas is coming into your property. If it is then call a Gas Safe engineer to test your system and isolate the fault.
 

Vaillant F.29 Boiler Fault Code

Error Description
Failure during operation: Re-ignition unsuccessful

Error Cause
Gas supply temporarily stopped, flue gas recirculation, condensate duct blocked, defective earthing of product, ignition transformer has spark failure.

Fix Vaillant F.29 Error Code
Check the gas supply into the property. If gas is coming into property then call a Gas Safe engineer to identify the issue. If gas isn’t coming into the property check with your gas provider.
 

Vaillant F.61 Boiler Fault Code

Error Description
Gas valve actuation fault

Error Cause
• Cable harness supply line to the gas valve is defective (short to earth, short circuit)
• Gas valve defective
• PCB defective

Fix Vaillant F.61 Error Code
Check the resistance across the gas valve for 50-54 ohms(+/-10%). If this is correct, then likely the PCB needs to be replaced. If the gas valve fails the resistance test, then likely the gas valve needs to be replaced.

 

Vaillant F.62 Boiler Fault Code

Error Description
Gas valve switch-off delay

Error Cause
• Delayed shutdown of gas valve detected– Secondary light (ignition and monitoring electrode indicates delayed extinguishing of the flame signal)
• Gas valve defective
• PCB defective

Fix Vaillant F.62 Error Code
Carry out a local tightness test on the gas valve. If gas tight then you may have to replace the PCB or replace the gas valve.
 

Vaillant F.63 Boiler Fault Code

Error Description
If you have a F63 fault code displayed on your Vaillant boiler, there is a problem with the circuit board (PCB). The PCB is what communicates with all electronic components.

Error Cause
• Old age; general wear and tear
• Connections to and from the PCB have worked loose, or have been damaged
• The PCB has not been setup correctly by a service engineer after a service, new boiler, or new PCB installation

Fix Vaillant F.63 Error Code
Usually this will require a new PCB which can cost between £350-£450. You may want to consider replacing your boiler if it is getting on in years.
 

Vaillant F.64 Boiler Fault Code

Error Description
If you have a F63 fault code displayed on your Vaillant boiler, there is a problem with the electrics.
• NTC thermistors on the flow and return boiler pipes
• Faulty connections
• PCB fault

Error Cause
• Short-circuit in flow
• Return NTC
• Electronics defective

Fix Vaillant F.64 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.65 Boiler Fault Code

Error Description
Main PCB Temperature Too High

Error Cause
• Mains Input Voltage Problem
• Damaged Or Loose Electrical Connection On The Main PCB
• Main PCB Fault

Fix Vaillant F.65 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.
 

Vaillant F.67 Boiler Fault Code

Error Description
Flame Signal Fault On The Main PCB

Error Cause
• Damaged Or Loose Electrical Connection On The Main PCB
• Main PCB Fault
• Mains Input Voltage Problem (Reverse Polarity, Poor Earth Etc)

Fix Vaillant F.67 Error Code
You will need a Gas Safe engineer to test your electronics and diagnose what part of the boiler electronics is generating the fault code.

Vaillant Ecomax Pro 828E Error Codes

The Vaillant ecoMAX pro is a High efficiency boiler that is not currently in production. 

The ecoMAX pro are regular boilers. Regular boilers are also known as open vent boilers because they are linked to an outside vent. The system provides central heating and hot water by using both a storage cylinder and water tank, which gives ultra-efficient operation. Due to the open vent they are not pressurised.

Vaillant F.00/F.04/F.05/F.10/F-14/F.15 Boiler Fault Code

Error Description
This fault according to the Vaillant Instructions and Servicing manual is a Heating Flow Temperature Sensor interruption or Heating Flow NTC Thermistor fault.

Error Cause
NTC (Negative Temperature Coefficient) plug not plugged in or has come loose, multiple plug on the PCB (Printed Circuit Board) not plugged in correctly, interruption in cable harness, NTC defective.

Fix Vaillant F.00/F.04/F.05/F.10/F.14/F.15 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.11 Boiler Fault Code

Error Description
This fault according to Vaillant Instructions and Servicing manual is a Heating Flow NTC Thermistor Fault or Heating Return NTC short circuit

Error Cause
There Is A Short Circuit On The Heating Return NTC Thermistor (Should Read 12Kohms @ 20C). Wiring Harness Fault Or Connection Error Between The Heating Return NTC Thermistor And The Main PCB.

Fix Vaillant F.11 Error Code
Check the NTC sensor. Check the wiring using a continuity tester and resistance tester if necessary. Replace NTC, harness or PCB as necessary.
 

Vaillant F.12 Boiler Fault Code

Error Description
Short circuit at cylinder charging sensor (NTC) only in combination with F.91

Error Cause
Sensor plug has a mass short to the casing. Short-circuit in wiring loom. Sensor faulty

Fix Vaillant F.12 Error Code
There is an issue with your heating flow thermister (NTC) and sensor plug, wiring loom and sensor will need to be tested for errors.
 

Vaillant F.13 Boiler Fault Code

Error Description
VU-/VUW boiler: Short circuit warm start sensor/cylinder sensor VUW boiler with actoSTOR: Short circuit cylinder sensor (NTC) only in combination with F.91

Error Cause
NTC defective, short circuit in cable harness, cable/casing

Fix Vaillant F.13 Error Code
There is an issue with your heating flow thermister (NTC) and it will either need to have the connecting cable replaced, the wiring harness replaced or the NTC itself will need to be replaced.
 

Vaillant F.21 Boiler Fault Code

Error Description
Pilot flame ignition failure

Error Cause
Defective ignition switch. Fault on PCB board. Defective gas valve.

Fix Vaillant F.21 Error Code
An engineer will need to check your system to diagnose the cause of the issue.
 

Vaillant F.22 Boiler Fault Code

Error Description
Safety switch-off: low water pressure. Shown on display as F.22

Error Cause
No pressure or water pressure too low in the boiler, water pressure sensor defective, cable to pump or water pressure sensor loose/not connected/defective

Fix Vaillant F.22 Error Code
1.Top up the pressure of the boiler or system using the internal filling loop if it is a combi boiler, otherwise using the external filling loop attached to the system.
2. The pressure sensor connection may have come out or become loose. Take the cable out, check it’s not broken and re-insert.
3. Check that the pump connection is not loose. If necessary remove the connection from the connector, check and re-insert.

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